During the Military Academy, she was close friends with Noel and Makoto. She's described as a straight A student, and has a rather no-nonsense personality. She's very serious and reserved, and is a member of the dignified Yayoi family. By the end of BlazBlue: Calamity Trigger's True Ending, she is assigned by Hazama to kill Noel and Jin. She originally appeared as a non-playable character in the Calamity Trigger Story Mode. In BlazBlue: Continuum Shift, Tsubaki heads to 13th Hierarchical City of Kagutsuchi to search for Jin Kisaragi and Noel Vermillion.

She uses an Ars Armagus called "Izayoi". When Tsubaki found Jin, he told her to get rid of Izayoi because it "steals the light from the user's eyes", implying it would, after a certain period of time, cause her to go blind.

Tsubaki is revealed to be a fan of Hakumen, going so far as to own all the books and movies based on the exploits of the Six Heroes.

In Hakumen's Story Mode, he indirectly reveals that in the past she had been his secretary instead of Noel. While they had more time together, he ultimately neglected her for his own exploits. She pleaded for him to stay when he had left, but continued on, and she was killed as a result. To remember the mistake he had made, he named one of his attacks in her honor. After her fight with Noel, Hazama tells Tsubaki that because of Noel's continued presence, she took Tsubaki's place as Jin's secretary, relegating Tsubaki herself into assassination tasks. Tsubaki, already slowly losing her sight due to overuse of Izayoi becomes depressed and angry at Noel, believing she stole everything from her (though Hazama left out that Tsubaki would have died anyway in the timeline where she is with Jin). Hazama uses the surfacing of these emotions to his advantage by having Phantom use its sorcery on Tsubaki to manipulate her jealousy for his own purposes. The critical point of her jealousy is reached when she pleads Jin to back down, telling him that she only wanted to be with him, and wishes Noel were dead. Ultimately rejected by Jin, Tsubaki sides with Hazama and the Imperator as her eyes turn red and her white clothes become black.